1. Field of Endeavor
The present disclosure relates to a protection coordination system, and more particularly to a protection coordination system configured to be used in an electric power distribution system.
2. Background
Generally, relay operating characteristics and their setting must be carefully coordinated in order to achieve selectivity. The aim is basically to switch off only the faulted component and to leave the rest of the power system in service in order to minimize supply interruptions and to assure stability.
Protection should be as sensitive as possible to detect faults at the lowest possible current level. At the same time, however, it should remain stable under all permissible load, overload and through-fault conditions.
FIG. 1 is an exemplary view illustrating an electric power distribution system according to prior art, and FIG. 2 is a graph illustrating a protection coordination method in a plurality of OCRs (Over Current Relays, 31, 32) in FIG. 1.
Referring to FIG. 1, the power distribution system includes the plurality of OCRs (31, 32) on a load line, and if a fault current occurs on the line, a circuit is switched to short-circuit for protection of the line, where the OCRs perform the protection coordination.
Referring to FIG. 2, the first OCR (31) performs an instantaneous trip operation at 40,000 A or more currents, and performs a timer action at 40,000 A or less. Furthermore, the second OCR (32) performs an instantaneous trip operation at 2,500 A or more currents, and performs a timer action at 2,500 A or less.
For example, in a case a current of 2,000 A is generated at ‘F’ point of FIG. 1, both the first and second OCRs (31 and 32) performs the timer action, where the second OCR (32) operates at approximately 0.2 second and the first OCR (31) operates at approximately 0.8 second.
Furthermore, in a case a current of 2,500 A is generated at ‘F’ point of FIG. 1, the second OCR (32) performs the instantaneous trip operation, and the first OCR (31) performs a timer action, such that the second OCR (32) instantly operates at 0.04 second while the first OCR (31) operates at approximately 0.5 second for protection coordination.
However, in a case a current of 5,000 A is generated at ‘F’ point of FIG. 1, both the first and second OCRs (31 and 32) operate almost at the same time (0.05 second and 0.04 second respectively) because the point is in an instantaneous operation section. That is, for smooth protection coordination, it is sufficient that only the second OCR (32) operates to remove an A section that includes the F point where the fault has occurred, but in this case, the first and second OCRs (31 and 32) simultaneously operate to remove a B section, causing a problem of removing a wide section.